JP7411417B2 - Hydraulic circuits, directional valves for hydraulic circuits and construction machinery - Google Patents

Description

The present invention relates to a hydraulic circuit, a directional control valve for the hydraulic circuit, and a construction machine.

Patent Document 1 discloses a hydraulic circuit that supplies oil to an actuator. This hydraulic circuit is applied to excavators, which are construction machines. The hydraulic circuit of Patent Document 1 employs an open center system. In this hydraulic circuit, in a neutral position where oil is not supplied to the actuator, oil discharged from the pump flows through the open center passage and into the tank. In the hydraulic circuit disclosed in Patent Document 1, a restriction is formed just before the tank in the open center passage, and the presence or absence of oil supply to the actuator can be determined from the pressure in the open center passage just before the restriction, so-called negative control pressure. Can be done. In Patent Document 1, when the negative control pressure increases, the amount of oil supplied from the pump is reduced, and when the negative control pressure decreases, the amount of oil supplied from the pump is increased.

Japanese Patent Application Publication No. 2011-52799

By the way, if oil is supplied to the actuator in an amount exceeding the allowable amount, the actuator may be damaged. Therefore, it is preferable that the capacity of the pump that supplies oil to the hydraulic circuit and the capacity of the actuator that is supplied with oil from the hydraulic circuit are set to a necessary size in consideration of the application of the hydraulic circuit and the like. On the other hand, due to various constraints in actual design and use, it may not be possible to prepare a pump or actuator with an appropriate capacity for each application.

In the hydraulic circuit disclosed in Patent Document 1, the amount of oil supplied from the pump can be adjusted depending on whether oil is supplied to any of the actuators. However, it is impossible to adjust the oil supply amount according to the load of the actuator to which oil is actually supplied.

The present invention has been made in consideration of the above points, and an object of the present invention is to make it possible to adjust the oil supply amount according to the load on the actuator.

The hydraulic circuit according to the invention comprises:
A passage is provided on an open center passage connected to a pump and supplies oil supplied from the pump to the actuator, and the passage is configured to subtract the pressure of the oil supplied to the actuator from the pressure of the oil supplied from the pump. a directional control valve that opens the open center passage when the differential pressure is greater than a set value;
a throttle provided on the downstream side of the directional switching valve in the open center passage;
A regulator that controls the pump according to the pressure of oil in the open center passage between the throttle and the directional control valve.

The hydraulic circuit according to the invention comprises:
another directional control valve provided on the open center passage and supplying oil supplied from the pump to another actuator;
a parallel passage that supplies oil discharged from the pump to the directional switching valve and the other directional switching valve in parallel;
The vehicle may further include a flow control valve provided on the parallel passage and adjusting the amount of oil supplied to the directional switching valve.

In the hydraulic circuit according to the present invention, the flow control valve may reduce the oil supply amount when a differential pressure obtained by subtracting the pressure on the upstream side of the flow control valve from the pressure on the downstream side of the flow control valve becomes large. good.

In the hydraulic circuit according to the present invention,
The directional control valve is
a valve body provided with an upstream port connected to the upstream side of the open center passage and a downstream port connected to the downstream side of the open center passage;
a spool that switches between blocking and opening between the upstream port and the downstream port by moving with respect to the valve body;
The device may further include a selector valve that opens and closes a bypass passage between the upstream port and the downstream port depending on the differential pressure.

In the hydraulic circuit according to the present invention, the selector valve may be supported inside the spool.

The directional valve according to the invention comprises:
an upstream port connected to the upstream side of the open center passage that is supplied with oil from the pump, a downstream port that is connected to the downstream side of the open center passage, an actuator port that leads to the actuator, and an actuator port that is supplied with oil from the pump. a valve body provided with a pump port, and a spool hole communicating with the upstream port, the downstream port, the actuator port, and the pump port;
The spool hole is movably accommodated in the spool hole, and has a position that opens the upstream port and the downstream port through the spool hole and blocks the actuator port and the pump port; a spool movable between a position where the upstream port and the downstream port are closed off and the actuator port and the pump port are opened;
A selector valve is provided that opens and closes a bypass passage connecting the upstream port and the downstream port depending on the pressure difference between the pressure in the actuator port and the pressure in the upstream port.

In the directional control valve according to the present invention, the selector valve may be supported inside the spool.

Another hydraulic circuit according to the invention comprises any of the directional valves according to the invention described above.

Yet another hydraulic circuit according to the invention includes:
an upstream port connected to the upstream side of the open center passage that is supplied with oil from the pump, a downstream port that is connected to the downstream side of the open center passage, an actuator port that leads to the actuator, a pump port that is supplied with oil from the pump, a valve body provided with a spool hole communicating with the upstream port, the downstream port, the actuator port and the pump port; and a position where the downstream port is opened and the actuator port and the pump port are disconnected, and the upstream port and the downstream port are disconnected through the spool hole, and the actuator port and the pump port are disconnected. a spool movable between the pump ports and an open position; and the upstream port and the downstream port depending on the pressure difference between the actuator port and the upstream port. a directional control valve having a selector valve that opens and closes a bypass passage connecting between the
a throttle provided on the downstream side of the directional switching valve in the open center passage;
A regulator that controls the pump according to the pressure of oil in the open center passage between the throttle and the directional control valve.

A construction machine according to the present invention includes any of the hydraulic circuits according to the present invention described above.

According to the present invention, the oil supply amount can be adjusted according to the load on the actuator.

FIG. 1 is a diagram for explaining one embodiment of the present invention, and is a diagram showing a construction machine, a hydraulic system, and a hydraulic circuit. FIG. 2 is a diagram showing the hydraulic circuit shown in FIG. 1 in a different state from that shown in FIG. FIG. 3 is a diagram showing the hydraulic circuit of FIG. 1 in a state different from that of FIGS. 1 and 2. FIG. FIG. 4 is a cross-sectional view showing a first directional valve that may be included in the hydraulic circuit of FIG. 1. FIG. FIG. 5 is a sectional view showing the first directional control valve of FIG. 4 in a different state from that of FIG. 4. FIG. FIG. 6 is a sectional view showing the first directional control valve of FIG. 4 in a state different from that of FIGS. 4 and 5. FIG.

Hereinafter, one embodiment of the present invention will be described with reference to specific examples shown in the drawings.

The hydraulic circuit 20 described below is a circuit that controls the flow of oil supplied from the pump P, and is applied to a machine for performing construction work, that is, the construction machine 10, as an example. Examples of construction machines 10 to which the hydraulic circuit 20 of this embodiment can be applied include excavators, crane trucks, forklifts, and the like. A hydraulic circuit 20 applied to the construction machine 10 constitutes a hydraulic system 15 with actuators A1 and A2 connected to mechanical equipment such as a shovel, a blade, a crane, a hammer, and a drive device. The hydraulic circuit 20 supplies oil to a hydraulic cylinder or a hydraulic motor serving as an actuator, and controls the operation of the actuator. The actuator operates to drive mechanical equipment. That is, the hydraulic system 15 includes a hydraulic circuit 20, a pump P that supplies pressure oil to the hydraulic circuit 20, and actuators A1 and A2 that are supplied with pressure oil from the hydraulic circuit 20. Construction machine 10 includes a hydraulic system 15 and mechanical equipment.

The hydraulic circuit 20 according to the present embodiment includes an open center passage CL supplied with oil from the pump P, a directional switching valve 40 provided on the open center passage CL, and a directional switching valve of the open center passage CL. It has a throttle 21 provided on the downstream side and a regulator 22 that controls the amount of oil supplied from the pump P according to the pressure in the open center passage CL between the throttle 21 and the directional switching valve 40. There is. That is, the hydraulic circuit 20 is configured as a circuit that performs negative control (negative control) that controls the discharge amount of the pump P according to the negative control pressure. Furthermore, in this embodiment, by adjusting the negative control pressure according to the load on the actuator A1 supplied with oil from the directional control valve 40, it is possible to adjust the discharge amount from the pump P according to the load on the actuator A1. are doing. That is, in combination with a circuit for realizing negative control, it is possible to effectively prevent the actuator A1 from being damaged by high loads.

1 to 3 show specific examples of a construction machine 10, a hydraulic system 15, and a hydraulic circuit 20 to which this embodiment is applied. 4-6 are cross-sectional views showing the directional control valve 40 included in the hydraulic circuit 20 of FIGS. 1-3. Hereinafter, this embodiment will be described by explaining specific examples shown in the drawings.

As shown in FIGS. 1 to 3, the illustrated hydraulic system 15 includes a pump P, a hydraulic circuit 20 supplied with oil (hydraulic oil) from the pump P, and the oil supply controlled by the hydraulic circuit 20. It has a first actuator A1, a second actuator A2, and a tank T that collects oil discharged from the hydraulic circuit 20. The hydraulic circuit 20 has an open center passage CL, a parallel passage PL, an actuator passage AL, and a tank passage TL as oil passages. The hydraulic circuit 20 includes a first directional switching valve 40 that controls the supply and discharge of oil to the first actuator A1, and a second directional switching valve 60 that controls the supply and discharge of oil to the second actuator A2. ing.

The open center passage CL and the parallel passage PL are connected to the pump P. The open center passage CL and the parallel passage PL are supplied with oil by being discharged from the pump P. A first directional switching valve 40 and a second directional switching valve 60 are provided on the open center passage CL. The open center passage CL is opened and closed by the first directional switching valve 40 and the second directional switching valve 60. Each directional switching valve 40, 60 opens the open center passage CL when it is in a neutral position where oil is not supplied to the corresponding actuator A1, A2. On the other hand, when each directional control valve 40, 60 is in an operating position supplying oil to the corresponding actuator A1, A2, it is possible to block the open center passage CL. In the illustrated example, the first directional switching valve 40 is located upstream of the second directional switching valve 60 along the oil flow path in the open center passage CL.

The open center passage CL communicates with the tank T at the most downstream side. Oil that is not supplied to the actuators A1, A2 via the directional control valves 40, 60 passes through the open center passage CL and is collected in the tank T. A throttle 21 is formed in the open center passage CL. The throttle 21 is located near the most downstream side of the open center passage CL. That is, the throttle 21 is located immediately in front of the tank T on the open center passage CL. Further, a pressure control valve 23 is provided in parallel to the throttle 21. The pressure control valve 23 forms a detour passage parallel to the throttle 21 when the pressure in the open center passage CL immediately before the throttle becomes greater than a preset valve opening pressure.

The parallel passage PL is connected to the first directional switching valve 40 and the second directional switching valve 60 as a parallel passage. The first directional switching valve 40 and the second directional switching valve 60 can be supplied with oil from the pump P via the parallel passage PL, regardless of their operating states. A check valve 24 is provided on the parallel passage PL.

The actuator passage AL extends between each directional control valve 40, 60 and the corresponding actuator A1, A2. Oil is supplied from the directional control valves 40, 60 to the corresponding actuators A1, A2 via the actuator passage AL. In the illustrated example, two actuator passages AL are provided between each directional control valve 40, 60 and the corresponding actuator A1, A2. One actuator passage AL is used to supply oil from the directional control valves 40, 60 to the actuators A1, A2, and in parallel, the other actuator passage AL is used to supply oil from the actuators A1, A2 to the directional control valves 40, 60. Used for draining oil.

Tank passage TL extends between each directional control valve 40, 60 and tank T. The oil discharged from the directional control valves 40 and 60 passes through the tank passage TL and is collected in the tank T.

The directional control valves 40 and 60 are supplied with oil from the pump P. The first directional switching valve 40 switches between opening and closing between the actuator passage AL leading to the first actuator A1, the parallel passage PL, and the tank passage TL. The first directional switching valve 40 controls supply and discharge of oil to the first actuator A1 by switching the flow path. Similarly, the second directional switching valve 60 switches between opening and closing between the actuator passage AL leading to the second actuator A2, the parallel passage PL, and the tank passage TL. The second directional switching valve 60 controls supply and discharge of oil to the second actuator A2 by switching the flow path. The first directional switching valve 40 and the second directional switching valve 60 are configured as spool valves as an example, although they are not particularly limited.

4 to 6 show a first directional valve 40 configured as a spool valve. The first directional valve 40 has a valve body 45 and a spool 50 as main components. The valve body 45 has a spool hole 45a that accommodates the spool 50. The spool 50 is arranged within the spool hole 45a. The spool 50 can move within the spool hole 45a along the longitudinal direction within the spool hole 45a. That is, the elongated rod-shaped spool 50 moves relative to the valve body 45 in its longitudinal direction.

In the illustrated example, the valve body 45 includes an upstream port UP, a downstream port LP, a first supply port 1PP, a second supply port 2PP, a first actuator port 1AP, a second actuator port 2AP, and a first tank port 1TP. and a second tank port 2TP. These ports all communicate with the spool hole 45a.

As schematically shown in FIG. 4, the upstream port UP is connected to the upstream side of the open center passage CL. In other words, the upstream port UP is connected to the side of the open center passage CL that is connected to the pump P. The downstream port LP is connected to the downstream side of the open center passage CL. In other words, the downstream port LP is connected to the side of the open center passage CL that is connected to the tank T.

The first actuator port 1AP communicates with one of the two actuator passages AL connected to the first directional valve 40. The second actuator port 2AP communicates with the other of the two actuator passages AL connected to the first directional valve 40. As shown in FIG. 4, a first supply port 1PP and a first tank port 1TP are provided on both sides of the first actuator port 1AP along the moving direction of the spool 50. Similarly, a second supply port 2PP and a second tank port 2TP are provided on both sides of the second actuator port 2AP. The first supply port 1PP and the second supply port 2PP communicate with each other. The first supply port 1PP and the second supply port 2PP both communicate with the parallel passage PL. The first tank port 1TP and the second tank port 2TP communicate with each other. The first tank port 1TP and the second tank port 2TP both communicate with the tank passage TL.

The spool 50 has a plurality of notches 50a and a plurality of lands 50b. The notch portion 50a is a portion whose width is reduced (diameter reduced) compared to the land portion 50b, and the land portion 50b is a portion whose width is expanded (diameter increased) compared to the notch portion 50a.

At the neutral position 40a of the first directional switching valve 40 shown in FIG. 4, one notch 50a of the spool 50 is located so as to straddle the upstream port UP and the downstream port LP. Therefore, the upstream port UP and the downstream port LP communicate through the spool hole 45a of the valve body 45 (the cutout 50a of the spool 50). That is, the first directional switching valve 40 in the neutral position 40a opens the open center passage CL.

At the neutral position 40a of the first directional switching valve 40, the spool hole 45a located between the first actuator port 1AP and the first supply port 1PP is closed by the land portion 50b of the spool 50. Further, in the neutral position 40a of the first directional switching valve 40, the spool hole 45a located between the first actuator port 1AP and the first tank port 1TP is closed by the land portion 50b of the spool 50. That is, at the neutral position 40a of the first directional valve 40, the first actuator port 1AP is blocked from both the first supply port 1PP and the first tank port 1TP. Similarly, in the neutral position 40a of the first directional valve 40, the second actuator port 2AP is blocked from both the second supply port 2PP and the second tank port 2TP. Therefore, the first directional switching valve 40 in the neutral position 40a blocks the actuator passage AL from both the parallel passage PL and the tank passage TL. That is, oil is not supplied to the first actuator A1, and oil is not discharged from the first actuator A1.

Next, FIG. 5 shows the first directional valve 40 in the first operating position 40b. In the first directional valve 40 in the first operating position 40b, the spool 50 has moved to the left in FIG. 5 with respect to the valve body 45. Moreover, FIGS. 2 and 3 show the hydraulic circuit 20 when the first directional switching valve 40 is in the first operating position 40b.

In the first operating position 40b of the first directional control valve 40 shown in FIG. ing. Therefore, the connection with the upstream port UP and the downstream port LP via the spool hole 45a (notch 50a of the spool 50) of the valve body 45 is cut off. That is, the first directional switching valve 40 in the first operating position 40b can close (block) the open center passage CL.

At the first operating position 40b of the first directional control valve 40, one notch 50a of the spool 50 is located so as to straddle the first actuator port 1AP and the first supply port 1PP. Therefore, the first actuator port 1AP and the first supply port 1PP communicate through the spool hole 45a of the valve body 45 (the cutout 50a of the spool 50). That is, the first directional switching valve 40 in the first operating position 40b connects the parallel passage PL and one actuator passage AL. Thereby, oil supplied from the parallel passage PL is supplied to the first actuator A1 via one actuator passage AL. Note that at the first operating position 40b of the first directional switching valve 40, the connection between the first actuator port 1AP and the first tank port 1TP is cut off.

Similarly, in the first operating position 40b of the first directional control valve 40, one notch 50a of the spool 50 is located so as to straddle the second actuator port 2AP and the second tank port 2TP. Therefore, the second actuator port 2AP and the second tank port 2TP communicate through the spool hole 45a of the valve body 45 (the cutout 50a of the spool 50). That is, the first directional switching valve 40 in the first operating position 40b connects the tank passage TL and the other actuator passage AL. Thereby, the oil discharged from the first actuator A1 flows into the tank passage TL via the other actuator passage AL, and is finally collected in the tank T. Note that at the first operating position 40b of the first directional switching valve 40, the connection between the second actuator port 2AP and the second supply port 2PP is cut off.

Next, FIG. 6 shows the first directional valve 40 in the second operating position 40c. In the first directional control valve 40 in the second operating position 40c, the spool 50 has moved to the right in FIG. 6 with respect to the valve body 45.

In the second operating position 40c of the first directional control valve 40 shown in FIG. ing. Therefore, the connection with the upstream port UP and the downstream port LP via the spool hole 45a (notch 50a of the spool 50) of the valve body 45 is cut off. That is, the first directional switching valve 40 in the second operating position 40c can close (block) the open center passage CL.

At the second operating position 40c of the first directional control valve 40, one notch 50a of the spool 50 is located so as to straddle the first actuator port 1AP and the first tank port 1TP. Therefore, the first actuator port 1AP and the first tank port 1TP communicate through the spool hole 45a of the valve body 45 (the cutout 50a of the spool 50). That is, the first directional switching valve 40 in the second operating position 40c connects the first tank port 1TP and one actuator passage AL. Thereby, oil discharged from the first actuator A1 flows into the tank passage TL via one actuator passage AL, and is finally collected in the tank T. Note that at the second operating position 40c of the first directional switching valve 40, the connection between the first actuator port 1AP and the first supply port 1PP is cut off.

Similarly, in the second operating position 40c of the first directional control valve 40, one notch 50a of the spool 50 is located so as to straddle the second actuator port 2AP and the second supply port 2PP. Therefore, the second actuator port 2AP and the second supply port 2PP communicate through the spool hole 45a of the valve body 45 (the cutout 50a of the spool 50). That is, the first directional switching valve 40 in the second operating position 40c connects the parallel passage PL and the other actuator passage AL. Thereby, oil supplied from the parallel passage PL is supplied to the first actuator A1 via the other actuator passage AL. Note that at the second operating position 40c of the first directional switching valve 40, the connection between the second actuator port 2AP and the second tank port 2TP is cut off.

Like the first directional switching valve 40, the second directional switching valve 60 can also take a neutral position 60a, a first operating position 60b, and a second operating position 60c. At the neutral position 60a, the second directional switching valve 60 opens the open center passage CL and stops supplying and discharging oil to the second actuator A2. The second directional switching valve 60 closes (cuts off) the open center passage CL in the first operating position 60b. The second directional control valve 60 in the first operating position 60b supplies oil to the second actuator A2 via one actuator passage AL, and discharges oil from the second actuator A2 via the other actuator passage AL. . The second directional switching valve 60 closes (cuts off) the open center passage CL in the second operating position 60c. The second directional control valve 60 in the second operating position 60c discharges oil from the second actuator A2 via one actuator passage AL, and supplies oil to the second actuator A2 via the other actuator passage AL. .

The illustrated hydraulic circuit 20 also includes a regulator 22 that controls the pump P according to the pressure within the open center passage CL. Regulator 22 communicates with open center passage CL via negative control passage NL. The negative control passage NL branches from the open center passage CL immediately upstream of the throttle 21. By connecting the regulator 22 to the end of the negative control passage NL opposite to the open center passage CL, the regulator 22 adjusts the oil pressure in the open center passage CL at a position immediately upstream of the throttle 21, that is, the negative control pressure. can be detected.

The regulator 22 is connected to a pump P that supplies oil to the hydraulic circuit 20, and controls the operation of the pump P based on the negative control pressure. As described above, when the directional control valves 40 and 60 are in the neutral position 40a, that is, when the oil supply to the actuators A1 and A2 is stopped, the flow rate per unit time in the open center passage CL increases. Negacon pressure increases. On the contrary, when either of the directional control valves 40, 60 is in the operating position, that is, when oil is supplied to either of the actuators A1, A2, the flow rate per unit time in the open center passage CL decreases. Negacon pressure decreases. Based on such fluctuations in negative control pressure, the regulator 22 increases the amount of oil supplied from pump P per unit time when negative control pressure decreases, and increases the amount of oil supplied from pump P per unit time when negative control pressure increases. Reduce.

As the pump P that supplies oil to the hydraulic circuit 20, various pumps that can change the amount of oil supplied per unit time can be employed. As an example, a variable capacity pump in which the inclination angle of the swash plate can be adjusted may be employed as the pump P that supplies oil to the hydraulic circuit 20.

Moreover, the first actuator A1 and the second actuator A2 that can be supplied with oil from the hydraulic circuit 20 are not particularly limited. In the illustrated example, the first actuator A1 is configured as a hydraulic motor that receives oil supply and outputs rotational motion. By setting the first directional switching valve 40 to the first operating position 40b, the hydraulic motor outputs rotational motion in one direction, and by setting the first directional switching valve 40 to the second operating position 40c, the hydraulic motor outputs rotational motion in the other direction. It is possible to output rotational motion in the direction. In application to the construction machine 10, as one specific example, the first actuator A1 can be a hydraulic motor that rotates the upper part of the excavator relative to the lower part. Furthermore, in the illustrated example, the second actuator A2 is configured as a hydraulic cylinder that receives oil supply and outputs linear motion. By setting the second directional switching valve 60 to the first operating position 60b, the hydraulic cylinder can move the rod forward, and by setting the second directional switching valve 60 to the second operating position 60c, the hydraulic cylinder can move the rod backward. . In application to the construction machine 10, as one specific example, a hydraulic cylinder that raises and lowers the arm of an excavator can be used as the second actuator A2.

By the way, as explained in the prior art section, if an actuator is supplied with an amount of oil that exceeds the allowable amount, the actuator may be damaged. More specifically, the pump pressure corresponding to the pressure of oil supplied to the directional control valve that controls the oil supply to the actuator is equal to the load pressure of the actuator corresponding to the pressure of oil supplied to the actuator. If it is too large, the actuator may be damaged.

In order to avoid damage to the actuator, the capacity of the pump that supplies oil to the hydraulic circuit and the capacity of the actuator that is supplied with oil from the hydraulic circuit are set to the necessary size taking into account the application of the hydraulic circuit, etc. It is preferable. However, due to various constraints in actual design and use, it may not be possible to prepare a pump or actuator with an appropriate capacity for each application. For example, if an attempt is made to reduce the number of pumps in a hydraulic system that includes a plurality of pumps, it may be necessary to include an actuator with a small capacity in a pump system with a large output. Furthermore, if a system that is supplied with oil from one pump includes a large number of actuators, it is possible that oil that exceeds the allowable amount may be supplied to the actuators depending on the number and combination of actuators that operate simultaneously.

Regarding this point, in this embodiment, it is possible to adjust the oil supply amount according to the load on the actuator. In the illustrated example, the amount of oil supplied from the pump P can be adjusted depending on the load on the first directional valve 40.

In a typical hydraulic excavator car, the load pressure of the hydraulic motor for swinging is low, and a large amount of oil is not required. On the other hand, the load pressure of the hydraulic cylinder that drives the arm is set high, and the amount of oil supplied to the hydraulic cylinder for driving the arm is also set high. Therefore, in the hydraulic circuit 20 that supplies oil from the same pump to the hydraulic cylinder for driving the arm and the hydraulic motor for swinging, the amount of oil supplied from the pump is adjusted in consideration of the load pressure of the hydraulic motor for swinging. This is very preferable in order to prevent damage to the hydraulic motor. The illustrated hydraulic circuit 20 is designed to control the supply and discharge of oil to the first directional valve 40 in consideration of the load condition of the first directional valve 40, which constitutes a hydraulic motor for swinging. .

As already explained, when the first directional control valve 40 provided on the open center passage CL is in the neutral position 40a shown in FIGS. When the supply to the actuator A1 is stopped, the open center passage CL is opened. As shown in FIG. 4, at the neutral position 40a, the notch 50a of the spool 50 is located so as to straddle the upstream port UP and the downstream port LP of the valve body 45. That is, the spool hole 45a widens to face the upstream port UP and the downstream port LP, and the upstream port UP and the downstream port LP communicate with each other via the spool hole 45a.

At this time, when the second directional control valve 60 is also in the non-operating position, the oil in the open center passage CL is collected in the tank T, and the negative control pressure corresponding to the oil pressure in the negative control passage NL increases. As the negative pressure increases, the regulator 22 controls the pump P to reduce the oil discharge amount.

Next, when the first directional control valve 40 is in the first operating position 40b shown in FIGS. 2 and 3, as shown in FIG. 5, the spool 50 faces the upstream port UP and the downstream port LP. The land portion 50b is located at the intermediate position, and the connection between the upstream port UP and the downstream port LP via the spool hole 45a, which had been established at the intermediate position, is interrupted. When the open center passage CL is closed, the negative control pressure decreases, and the regulator 22 controls the pump P to increase the oil discharge amount. Thereby, a sufficient amount of oil can be supplied from the first directional control valve 40 located at the first operating position 40b to the first actuator A1.

In this way, oil is supplied to the first actuator A1, but if the pump pressure becomes too large relative to the load pressure of the first actuator A1, there is a possibility that the first actuator A1 will be damaged. . In other words, if the differential pressure obtained by subtracting the oil pressure (load pressure) supplied to the first actuator A1 from the oil pressure (pump pressure) supplied from the pump P to the first directional control valve 40 becomes too large, the 1 actuator A1 may be damaged.

Therefore, when the differential pressure obtained by subtracting the load pressure from the pump pressure is smaller than the set value (switching value) (or less than the set value), the first directional valve 40 is switched to the open center passage as shown in FIG. CL remains closed. On the other hand, when the differential pressure obtained by subtracting the load pressure from the pump pressure is larger than the set value (switching value) (or is greater than or equal to the set value), the first directional switching valve 40 opens the open center passage CL. In particular, in the illustrated example, as shown in FIG. 3, if the differential pressure obtained by subtracting the load pressure from the pump pressure is greater than (or greater than) a set value (switching value), the first directional valve 40 opens the open center passage CL in a constricted state. When the open center passage CL is closed, the negative control pressure decreases and the amount of oil supplied from the pump P per unit time increases. On the other hand, when the open center passage CL is opened, oil begins to flow through the open center passage CL. Further, when the open center passage CL is opened in a constricted state, a smaller amount of oil flows through the open center passage CL than when the open center passage CL is fully opened.

In the following, an example will be described in which the open center passage CL is switched between closing and opening in a constricted state based on the differential pressure obtained by subtracting the load pressure from the pump pressure, but the present invention is not limited to this example. The open center passage CL may be switched between closing and opening based on the differential pressure obtained by subtracting the load pressure from the pump pressure. By switching between closing and opening the open center passage CL, it is possible to obtain the same effect as switching between closing and opening the open center passage CL in a constricted state.

The negative control pressure when the open center passage CL is narrowed is higher than the negative control pressure when the open center passage CL is closed, and lower than the negative control pressure when the open center passage CL is opened (fully opened). The amount of oil supplied from the pump P to the first directional valve 40 when the open center passage CL is throttled is smaller than the amount of oil supplied when the open center passage CL is closed, and the open center passage CL is opened. The amount of oil supplied will be higher than the amount of oil supplied when the engine is fully opened. Therefore, when the load pressure of the first actuator A1 is too low relative to the pump pressure, the amount of oil supplied from the pump P to the open center passage CL and the parallel passage PL is reduced. This effectively prevents an excessive amount of oil from flowing into the first actuator A1 via the first directional switching valve 40, making it possible to avoid damage to the first actuator A1.

In the illustrated example, the first directional valve 40 includes a first selector valve 56 . The first selector valve 56 opens and closes the bypass passage BL that connects the upstream port UP and the downstream port LP. The first selector valve 56 is movable between a closed position and a throttle position (open position). In the closed position shown in FIG. 2, the first selector valve 56 blocks communication between the upstream port UP and the downstream port LP. In the throttle position (open position) shown in FIG. 3, the first selector valve 56 connects the upstream port UP and the downstream port LP in a throttled state.

In the illustrated example, the first selector valve 56 receives the pressure in the oil supply path from the first directional valve 40 to the first actuator A1 as a pilot pressure, which corresponds to the load pressure, and is pushed toward the shutoff position. . Further, the first selector valve 56 receives pressure in the oil supply path from the pump P to the first directional control valve 40 as a pilot pressure, which corresponds to the pump pressure, and is pushed toward the throttle position. Furthermore, the first directional switching valve 40 has a first pressing member 58 that pushes the first selector valve 56 toward the shutoff position. The strength of the pressing force exerted by the first pressing member 58 determines the set value (switching value) of the differential pressure for switching between blocking and throttling (opening) the open center passage CL.

Note that the first selector valve 56 switches between blocking and throttling the open center passage CL when the first directional switching valve 40 is in the first operating position 40b. On the other hand, as shown in FIGS. 1 to 3, the first directional switching valve 40 has a second selector valve 57. The second selector valve 57 switches between blocking and throttling the open center passage CL when the first directional switching valve 40 is in the second operating position 40c. That is, even when the first directional switching valve 40 provided on the open center passage CL is in the second operating position 40c, it supplies oil to the first actuator A1 in the same way as when it is in the first operating position 40b. At this time, if the differential pressure obtained by subtracting the load pressure of the first actuator A1 from the pump pressure of the oil supplied to the first directional valve 40 is smaller than the set value (or if it is less than the set value), the open center passage CL is shut off, and when the differential pressure is larger than the set value (or when it is greater than or equal to the set value), the open center passage CL is opened in a constricted state.

Here, the configuration related to the first selector valve 56 and the second selector valve 57 will be described in further detail with reference to specific examples shown in FIGS. 4 to 6.

Note that FIG. 5 shows a cross section of the first directional control valve 40 in the first operating position 40b. Above the centerline of the first directional valve 40 in FIG. 5, the first selector valve 56 is shown in the throttle position. Below the centerline of the first directional valve 40 in FIG. 5, the first selector valve 56 is shown in the closed position. In the example shown in FIG. 5, the position of the first selector valve 56 closer to the right is the throttle position, and the position of the first selector valve 56 closer to the left is the closed position.

As shown in FIG. 5, the spool 50 is provided with a first hole 51 extending along its axial direction. The first selector valve 56 is disposed within the first hole 51 so as to be movable along the axial direction of the spool 50. A first pressing member 58 is also provided within the first hole 51 . The first pressing member 58 pushes the first selector valve 56 from the throttle position to the closed position. Further, the spool 50 has a first connection port 51a, a second connection port 51b, and a third connection port 51c extending between the surface forming the land portion 50b and the inner surface forming the first hole 51. The first connection port 51a, the second connection port 51b, and the third connection port 51c each extend in a direction non-parallel to the axial direction of the spool 50, typically in a direction perpendicular to the axial direction of the spool 50.

As shown in FIG. 5, when the spool 50 is in the first operating position 40b, the first connection port 51a opens to the first actuator port 1AP. The oil in the first actuator port 1AP flows into the first hole 51 through the first connection port 51a and acts on one end surface 56a of the first selector valve 56. The pressure acting on one end surface 56a of the first selector valve 56, together with the first pressing member 58, pushes the first selector valve 56 from the throttle position to the closed position (towards the left in FIG. 5). The first pressing member 58 may be made of an elastic material such as a spring member, for example. The first actuator port 1AP forms an oil passage for oil supplied to the first actuator A1. Therefore, the pressure in the first actuator port 1AP that pushes the first selector valve 56 toward the closed position corresponds to the load pressure of the first actuator A1.

When the spool 50 is in the first operating position 40b, the second connection port 51b opens to the upstream port UP. Further, the second connection port 51b faces the first valve passage 56x of the first selector valve 56, regardless of the position of the first selector valve 56. The first valve passage 56x of the first selector valve 56 extends between the side surface of the first selector valve 56 and the other end surface 56b of the first selector valve 56. More specifically, the first valve passage 56x includes a surface recess 56xa extending in the moving direction of the first selector valve 56 so as to face the second connection port 51b regardless of the position of the first selector valve 56; It has an internal hole 56xb that opens in the other end surface 56b of the selector valve 56 and extends in the moving direction of the first selector valve 56, and a communication hole 56xc that connects the recess 56xa and the internal hole 56xb. The first valve passage 56x of the first selector valve 56 forms a bypass passage BL that is opened and closed depending on the position of the first selector valve 56.

The oil in the upstream port UP flows into the first hole 51 via the second connection port 51b and the first valve passage 56x, and acts on the other end surface 56b of the first selector valve 56. The pressure acting on the other end surface 56b of the first selector valve 56 pushes the first selector valve 56 from the closed position toward the throttle position (toward the right in FIG. 5). The upstream port UP forms an oil passage for oil supplied from the pump P to the first directional switching valve 40. Therefore, the pressure within the upstream port UP that pushes the first selector valve 56 toward the throttle position corresponds to the pump pressure.

When the spool 50 is in the first operating position 40b, the third connection port 51c opens to the downstream port LP. The third connection port 51c is closed by the side surface of the first selector valve 56 when the first selector valve 56 is in the closed position. On the other hand, the third connection port 51c faces a region of the first hole 51 defined by the other end surface 56b of the first selector valve 56 when the first selector valve 56 is in the throttle position. This region communicates with the upstream port UP via the first valve passage 56x and the second connection port 51b, and the oil in the upstream port UP flows into this region.

Note that, as shown in FIG. 4, when the spool 50 is in the neutral state 40a, the first selector valve 56 and the second selector valve 57 are both located in the closed position.

With the above configuration, when the first directional control valve 40 is in the first operating position 40b, the oil in the first actuator port 1AP acts on one end surface 56a of the first selector valve 56, and the first selector valve 56 Oil in the upstream port UP acts on the other end surface 56b. Therefore, the first selector valve 56 is pushed toward the closed position from the throttle position side by the force corresponding to the load pressure of the actuator and the pushing force of the first pressing member 58. Further, the first selector valve 56 is pushed toward the throttle position from the closed position side by a force corresponding to the pump pressure. When the differential pressure obtained by subtracting the actuator load pressure from the pump pressure is smaller than the preset pushing force of the first pushing member 58, the first selector valve 56 is maintained in the closed position. At this time, since the third connection port 51c is blocked by the first selector valve 56, the first valve passage 56x of the first selector valve 56 does not communicate with the downstream port LP, so the bypass passage BL is blocked ( (closed). Conversely, when the differential pressure obtained by subtracting the actuator load pressure from the pump pressure is greater than the preset pushing force of the first pressing member 58, the first selector valve 56 is maintained at the throttle position. At this time, the second connection port 51b, the first valve passage 56x, the first hole 51, and the third connection port 51c form a bypass passage BL that connects the upstream port UP and the downstream port LP in a constricted state. .

Next, referring mainly to FIG. 6, the configuration related to the second selector valve 57 will be described in detail. FIG. 6 shows a cross section of the first directional valve 40 in the second operating position 40c. The second selector valve 57 is shown in the throttle position above the center line of the first directional control valve 40 in FIG. The second selector valve 57 is shown in the closed position below the centerline of the first directional valve 40 in FIG. In the example shown in FIG. 6, the position of the second selector valve 57 closer to the right is the closed position, and the position of the second selector valve 57 closer to the left is the throttle position.

As shown in FIG. 6, the spool 50 is provided with a second hole 52 extending along its axial direction. The second selector valve 57 is disposed within the second hole 52 so as to be movable along the axial direction of the spool 50. A second pressing member 59 is also provided within the second hole 52 . The second pressing member 59 pushes the second selector valve 57 from the throttle position to the closed position. The second pressing member 59 may be made of an elastic material such as a spring member, for example. Furthermore, the spool 50 has a fourth connection port 52a, a fifth connection port 52b, and a sixth connection port 52c extending between the surface forming the land portion 50b and the inner surface forming the second hole 52. The fourth connection port 52a, the fifth connection port 52b, and the sixth connection port 52c each extend in a direction non-parallel to the axial direction of the spool 50, typically in a direction perpendicular to the axial direction of the spool 50.

As shown in FIG. 6, when the spool 50 is in the second operating position 40c, the fourth connection port 52a opens to the second actuator port 2AP. Further, an internal passage (not shown) is formed in the spool 50 so that the fourth connection port 52a communicates with the second hole 52. Therefore, the oil in the second actuator port 2AP flows into the second hole 52 through the fourth connection port 52a and acts on one end surface 57a of the second selector valve 57. The pressure acting on one end surface 57a of the second selector valve 57, together with the second pressing member 59, pushes the second selector valve 57 from the throttle position to the closed position (toward the right side in FIG. 6). The second actuator port 2AP forms an oil passage for oil supplied to the first actuator A1. Therefore, the pressure in the second actuator port 2AP that pushes the second selector valve 57 toward the closed position corresponds to the load pressure of the first actuator A1.

When the spool 50 is in the second operating position 40c, the sixth connection port 52c opens to the upstream port UP. The oil in the upstream port UP flows into the second hole 52 through the sixth connection port 52c and acts on the other end surface 57b of the second selector valve 57. The pressure acting on the other end surface 57b of the second selector valve 57 pushes the second selector valve 57 from the closed position toward the throttle position (towards the left in FIG. 6). The upstream port UP forms an oil passage for oil supplied from the pump P to the first directional switching valve 40. Therefore, the pressure within the upstream port UP that pushes the first selector valve 56 toward the throttle position corresponds to the pump pressure.

When the spool 50 is in the second operating position 40c, the fifth connection port 52b opens to the downstream port LP. This fifth connection port 52b is closed by the side surface of the second selector valve 57 when the second selector valve 57 is in the closed position. On the other hand, the fifth connection port 52b faces the second valve passage 57x of the second selector valve 57 when the second selector valve 57 is in the throttle position. In the illustrated example, the second valve passage 57x is formed by a recess provided on the side surface of the second selector valve 57 and extending along the moving direction of the second selector valve 57. This recess extends to the other end surface 57b of the second selector valve 57 and communicates with a region within the second hole 52 defined by the other end surface 57b of the second selector valve 57. The second valve passage 57x formed of a concave portion forms an oil flow path extending along the moving direction of the second selector valve 57 between the outer surface of the second selector valve 57 and the inner surface of the second hole 52. The second valve passage 57x of the second selector valve 57 forms a bypass passage BL that is opened and closed depending on the position of the second selector valve 57.

With the above configuration, when the first directional control valve 40 is in the second operating position 40c, the oil in the second actuator port 2AP acts on one end surface 57a of the second selector valve 57, and the second selector valve 57 Oil in the upstream port UP acts on the other end surface 57b. Therefore, the second selector valve 57 is pushed toward the closed position from the throttle position side by the force corresponding to the load pressure of the actuator and the pushing force of the second pressing member 59. Further, the second selector valve 57 is pushed toward the throttle position from the closed position side by a force corresponding to the pump pressure. When the differential pressure obtained by subtracting the actuator load pressure from the pump pressure is smaller than the preset pushing force of the second pressing member 59, the second selector valve 57 is maintained in the closed position. At this time, since the fifth connection port 52b does not communicate with the second valve passage 57x, the bypass passage BL is blocked (closed). Conversely, when the differential pressure obtained by subtracting the actuator load pressure from the pump pressure is greater than the preset pushing force of the second pressing member 59, the first selector valve 56 is maintained at the throttle position. At this time, the fifth connection port 52b, the second valve passage 57x, the second hole 52, and the sixth connection port 52c form a bypass passage BL that connects the upstream port UP and the downstream port LP in a constricted state. .

By the way, in the example shown in FIGS. 1 to 3, the hydraulic circuit 20 includes a flow control valve 25 that is provided on the parallel passage PL and adjusts the amount of oil supplied to the first directional control valve 40. ing. The flow control valve 25 reduces the flow rate of oil per unit time when the differential pressure obtained by subtracting the pressure on the upstream side of the flow control valve 25 from the pressure on the downstream side of the flow control valve 25 becomes large. In the illustrated hydraulic circuit 20, by using the flow rate control valve 25, it is also possible to adjust the amount of oil supplied to the first actuator A1 via the first directional switching valve 40. As an example of the flow control valve 25, the valve disclosed in JP2017-215004A can be used. In the illustrated example, when the second directional switching valve 60 is in the operating position and oil is supplied to the second actuator A2, the open center passage CL is closed. As a result, the negative control pressure decreases and the amount of oil supplied from the pump P increases. However, by providing the flow control valve 25, even in a situation where the first actuator A1 and the second actuator A2 operate in parallel, the pump pressure can be prevented from becoming too high relative to the load pressure of the first actuator A1. can be avoided. Thereby, damage to the actuator can be effectively prevented.

In the embodiment described above, the hydraulic circuit 20 is provided on the open center passage CL and the open center passage CL to which oil is supplied from the pump P. 1 actuator) A directional control valve ( 40, the throttle 21 provided downstream of the directional valve 40 in the open center passage CL, and the pressure in the open center passage CL between the throttle 21 and the directional valve 40. and a regulator 22 that controls the amount of oil supplied from the pump P.

In this embodiment, the directional control valve 40 opens the open center passage CL when the oil supplied from the pump P to the actuator A1 is stopped, and supplies oil to the actuator A1 and changes the direction. Open center occurs when the differential pressure obtained by subtracting the oil pressure (load pressure) supplied from the switching valve 40 to the actuator A1 from the oil pressure (pump pressure) supplied from the pump P to the directional switching valve is smaller than the set value. The passage CL is shut off, oil is supplied to the actuator, and the open center passage is throttled when the differential pressure obtained by subtracting the load pressure of the actuator from the pump pressure supplied from the pump is larger than a set value.

According to this embodiment, pump pressure corresponding to the pressure of oil supplied to the directional control valve (first directional control valve) 40 is supplied from the directional control valve 40 to the actuator (first actuator) A1. If the load pressure of the actuator is too large, the directional control valve 40 opens the open center passage CL while constricting it. Therefore, if the actuator load pressure is too low relative to the pump pressure, the open center passage CL is opened and a limited amount of oil flows through the open center passage CL. As oil flows through the open center passage CL, the negative control pressure increases, and the regulator 22 reduces the amount of oil supplied from the pump P per unit time. That is, the amount of oil supplied from the pump P per unit time can be adjusted according to the load on the actuator (first actuator) A1, thereby reducing the pump pressure and effectively preventing damage to the actuator A1. can do.

In one specific example of the embodiment described above, the directional switching valve (first directional switching valve) 40 has an upstream port UP connected to the upstream side of the open center passage CL and an upstream side port UP connected to the downstream side of the open center passage CL. A valve body 45 provided with a downstream port LP, a spool 50 that switches disconnection and connection between the upstream port UP and the downstream port LP by moving with respect to the valve body 45, and It has selector valves (first selector valve, second selector valve) 56, 57 that open and close the bypass passage BL connecting the side port LP according to the differential pressure. According to this specific example, the pump pressure and load pressure to be monitored can be used as pilot pressures for operating the selector valves 56 and 57. Therefore, with a simple configuration, the amount of oil supplied from the pump per unit time can be adjusted with high precision according to the load on the actuator A1.

In a specific example of the embodiment described above, the selector valves (first selector valve, second selector valve) 56 and 57 are supported inside the spool 50. According to this specific example, while effectively suppressing the increase in size of the directional valve switching valve (first actuator) A1, the amount of power from the pump P per unit time is adjusted according to the load of the actuator (first actuator) A1. Oil supply amount can be adjusted.

In the embodiment described above, the directional control valve 40 for the hydraulic circuit includes a valve body 45, a spool 50, and selector valves 56, 57. The valve body 45 has an upstream port UP connected to the upstream side of the open center passage CL to which oil is supplied from the pump P, a downstream port LP connected to the downstream side of the open center passage CL, and an actuator (first actuator). ) Actuator ports 1AP, 2AP leading to A1, pump ports 1PP, 2PP supplied with oil from pump P, upstream port UP, downstream port LP, actuator ports 1AP, 2AP, and pump ports 1PP, 2PP. A spool hole 45a is provided. The spool 50 is movably housed in the spool hole 45a. The spool 50 has a position where it connects the upstream port UP and the downstream port LP through the spool hole 45a and blocks the actuator ports 1AP, 2AP and the pump ports 1PP, 2PP, and a position where the upstream port UP through the spool hole 45a connects the upstream port UP and the downstream port LP. and a position where the downstream port LP is disconnected and the actuator ports 1AP, 2AP and the pump ports 1PP, 2PP are connected. The selector valves 56 and 57 open and close the bypass passage BL connecting the upstream port UP and the downstream port LP depending on the pressure difference between the pressure in the actuator ports 1AP and 2AP and the pressure in the upstream port UP.

According to this embodiment, the pump pressure corresponding to the oil pressure in the upstream port UP of the directional control valve (first directional control valve) 40 communicating with the open center passage CL is applied to the actuator (first actuator) A1. When the load pressure corresponding to the oil pressure in the actuator ports 1AP, 2AP of the directional control valve 40 leading to Open. Therefore, if the actuator load pressure is too low relative to the pump pressure, the open center passage CL is opened and a limited amount of oil flows through the open center passage CL. According to such a directional control valve 40, in combination with control of the oil supply amount using negative control pressure (negative control), the oil supply amount per unit time from the pump P can be adjusted according to the load of the actuator A1. Thus, damage to the actuator A1 can be effectively prevented.

In one specific example of the embodiment described above, selector valves 56 and 57 are supported within spool 50. According to this specific example, while effectively suppressing the increase in size of the directional switching valve (first directional switching valve) 40, the amount of power from the pump per unit time is adjusted according to the load of the actuator (first actuator) A1. Oil supply amount can be adjusted.

Although one embodiment has been described with reference to illustrative examples, these examples are not intended to limit the embodiment. The embodiment described above can be implemented in various other specific examples, and various omissions, substitutions, changes, additions, etc. can be made without departing from the gist thereof.

For example, although a configuration has been described in which the bypass passage BL is opened and closed according to the differential pressure between the load pressure of the actuator and the pump pressure, the above-described configuration is merely an example. For example, the first valve passage 56x, the second valve passage 57x, the first connection port 51a, the second connection port 51b, the third connection port 51c, the fourth connection port 52a, the fifth connection port 52b, and the sixth connection port 52c. The structure and arrangement can be changed in various ways depending on the structure of the spool 50 and the valve body 45.

Further, as already explained, an example has been shown in which the open center passage is opened in a constricted state depending on the differential pressure between the load pressure of the actuator and the pump pressure, but the present invention is not limited to this example. When opening the open center passage according to the differential pressure between the load pressure of the actuator and the pump pressure, the open center passage may be opened without being throttled. Even in such an example, the effects of the present embodiment described above can be achieved.

10 Construction machine 15 Hydraulic system 20 Hydraulic circuit 22 Regulator 21 Throttle 23 Pressure control valve 24 Check valve 25 Flow control valve 40 First directional valve 40a Neutral position 40b First operating position 40c Second operating position 45 Valve body 45a Spool hole 50 Spool 50a Notch 50b Land portion 51 First hole 51a First connection port 51b Second connection port 51c Third connection port 52 Second hole 52a Fourth connection port 52b Fifth connection port 52c Sixth connection port 56 First selector Valve 56a End face 56b End face 56x First valve passage 56xa Recess 56xb Internal hole 56xc Communication hole 57 Second selector valve 57a End face 57b End face 57x Second valve passage 58 First pressing member 59 Second pressing member 60 Second directional switching valve P Pump A1 First actuator A2 Second actuator T Tank BL Bypass passage NL Negative control passage CL Open center passage PL Parallel passage AL Actuator passage TL Tank passage UP Upstream port LP Downstream port 1PP First supply port 2PP Second supply port 1AP 1 actuator port 2AP 2nd actuator port 1TP 1st tank port 2TP 2nd tank port

Claims (9)

a passage provided on an open center passage connected to a pump and connected to a parallel passage connected to the pump for supplying oil supplied from the pump to the actuator, the pressure of the oil supplied to the actuator; a directional control valve that opens the open center passage when a differential pressure subtracted from the pressure of oil supplied from the pump is greater than a set value;
Another directional control valve that is provided downstream of the directional control valve on the open center passage and has a passage that is connected to the parallel passage and supplies oil supplied from the pump to another actuator;
a throttle provided on the downstream side of the another directional control valve in the open center passage;
A hydraulic circuit, comprising: a regulator that controls the pump depending on the pressure of oil in the open center passage between the throttle and the another directional valve. The directional control valve is
a valve body provided with an upstream port connected to the upstream side of the open center passage and a downstream port connected to the downstream side of the open center passage;
a spool that switches between blocking and opening between the upstream port and the downstream port by moving with respect to the valve body;
The hydraulic circuit according to claim 1, further comprising a selector valve that opens and closes a bypass passage between the upstream port and the downstream port according to the differential pressure. 3. The hydraulic circuit of claim 2, wherein the selector valve is supported within the spool. an upstream port connected to the upstream side of the open center passage to which oil is supplied from the pump; a downstream port connected to the downstream side of the open center passage; and an actuator connected to the parallel passage to which oil is supplied from the pump. a valve body provided with an actuator port that communicates with the pump, a pump port that is supplied with oil from the pump, and a spool hole that communicates with the upstream port, the downstream port, the actuator port, and the pump port;
The spool hole is movably accommodated in the spool hole, and has a position that opens the upstream port and the downstream port through the spool hole and blocks the actuator port and the pump port; a spool movable between a position where the upstream port and the downstream port are closed off and the actuator port and the pump port are opened;
for a hydraulic circuit, comprising: a selector valve that opens and closes a bypass passage connecting the upstream port and the downstream port according to a pressure difference between the pressure in the actuator port and the pressure in the upstream port; directional valve. The directional control valve for a hydraulic circuit according to claim 4, wherein the selector valve is supported inside the spool. A hydraulic circuit comprising the directional control valve according to claim 4 or 5. An upstream port that connects to the upstream side of the open center passage that is supplied with oil from the pump, a downstream port that connects to the downstream side of the open center passage, and a downstream port that connects to the parallel passage that is supplied with oil from the pump and leads to the actuator. An actuator port, a pump port to which oil is supplied from the pump, the upstream port, the downstream port, and a valve body provided with a spool hole communicating with the actuator port and the pump port, movable to the spool hole. a position where the upstream port and the downstream port are opened through the spool hole and the actuator port and the pump port are closed off; a spool movable between a position that closes off between the downstream ports and opens between the actuator port and the pump port; and a difference between the pressure in the actuator port and the pressure in the upstream port. a directional switching valve having a selector valve that opens and closes a bypass passage connecting the upstream port and the downstream port according to pressure;
Another directional control valve that is provided downstream of the directional control valve on the open center passage and has a passage that is connected to the parallel passage and supplies oil supplied from the pump to another actuator;
a throttle provided on the downstream side of the another directional control valve in the open center passage;
A hydraulic circuit, comprising: a regulator that controls the pump depending on the pressure of oil in the open center passage between the throttle and the another directional valve. The hydraulic circuit according to any one of claims 1, 2, 3, and 7, further comprising a flow control valve provided on the parallel passage and adjusting the amount of oil supplied to the directional control valve. A construction machine comprising the hydraulic circuit according to any one of claims 1, 2, 3, 6, 7 and 8 .